Milling method used for producing structural components

ABSTRACT

The invention relates to milling methods for the production of structural components of materials that are difficult to machine by chip-cutting. A milling tool with a tool radius is rotationally driven about an axis of the milling tool to ensure a central rotation thereof, whereby a reference point of the milling tool preferably lying on the axis is moved on several curved paths, whereby the paths preferably comprise different curvatures, and whereby the milling tool is moved on the paths with a radial miller feed relative to the material. According to the invention, the curvature in each path point of each path is determined in such a manner that an optimized circumferential contact of the milling tool is ensured for each path point.

The invention relates to a milling method for the production ofstructural components according to the preamble of the patent claim 1.

The present invention relates to the field of milling technology,especially the HSC milling (High Speed Cutting milling), which is alsodesignated as HPC milling (High Performance Cutting milling), and namelythe case of the so-called trochoidal milling.

In so-called trochoidal milling, a milling tool or a miller, whichcomprises a certain tool radius, is rotationally driven about an axis ofthe miller to ensure a central rotation of the miller. A reference pointof the miller, which preferably lies on the axis, is moved on a curvedpath or track simultaneously to the milling processing or machining,whereby this path is circular in shape according to the prior art inconventional trochoidal milling. A translational feed advance motion ofthe reference point is superimposed on the motion of the milling tool orof the miller along this path. The superposition of these three motionsof the milling tool, i.e. the superposition of the central rotation ofthe milling tool about its axis, with the motion of the reference pointof the milling tool on a circular path, and with the translational feedadvance motion of the reference point of the milling tool, results in amotion of the milling tool in the sense of a trochoid or cycloid.

For a stable milling process in the trochoidal milling it is significantthat the maximum permissible cutting forces on the milling tool are notexceeded. Moreover, the cutting chips that arise during the milling mustbe so characterized with respect to chip thickness and chip length, sothat the chips can be carried away without problems via the channels ofthe milling tool. In order to ensure this, the parameters that arerelevant for the trochoidal milling: radius of the milling tool; radiusof the circular paths on which the reference point of the miller ismoved; miller feed advance; cutting tooth feed of the miller; aredimensioned and maintained constant over the entire milling processingor machining, so that over the entire milling processing or machining onthe one hand the permissible cutting forces are not exceeded and on theother hand the cutting chips can always be carried away well. From this,however, according to the prior art, there results a strongly varying orchanging circumferential wrapping contact of the miller. From this itfollows that the effectiveness of the milling processing or machining islimited in trochoidal milling known from the prior art. Disadvantagesarise with respect to milling time and operating service life of themilling tool.

Starting from this point, the underlying problem on which the presentinvention is based, is to propose a novel milling method for theproduction of structural components.

This problem is solved in that the above initially mentioned millingmethod is further developed by the features of the characterizing partof the patent claim 1.

According to the invention, the curvature at each path point of eachpath is determined such that an optimized circumferential (wrapping)contact of the milling tool is ensured for each path point. Hereby themilling time can be reduced. Moreover, the operating lifetime or theuseful operating time of the milling tool is increased, because thecutting entries of the cutting edges of the milling tool for carryingout the milling processing or machining are reduced.

According to an advantageous embodiment of the invention, at thebeginning or at the start of each path, the milling tool is moved intothe material to be milled in such a manner, so that a path vector of themilling tool extends in a tangential direction relative to a sidewallthat is to be milled of the structural component that is to be produced.The milling tool is moved into the material in this direction for solong until the maximum permissible circumferential contact of themilling tool is reached. After reaching the maximum permissiblecircumferential contact, the path vector of the milling tool andtherewith the curvature at each path point is adjusted as a function ofthe tool radius of the milling tool, as a function of the desiredsidewalls or depressions or recesses, and as a function of the raw partcontour or a milled contour of the previously completed milling path,such that approximately the maximum permissible circumferential contactof the milling tool will be maintained in each subsequent path point ofthe path. Preferably, the maximum permissible circumferential contact ofthe milling tool is ensured in each subsequent path point of the pathexcept for an exit region of the milling tool, in which the miller ismoved out of the material to be milled.

Preferred further embodiments of the invention follow from the dependentclaims and from the following description.

An example embodiment of the invention, without being limited hereto, isexplained in further detail in connection with the drawing. In thedrawing:

FIG. 1 shows a strongly schematized illustration for the explanation ofthe trochoidal milling according to the prior art;

FIG. 2 shows the circumferential contact of the milling tool that occursin the trochoidal milling according to the prior art;

FIG. 3 shows a sharply schematized illustration of a flow channel thatis bounded by two curved sidewalls and that is to be milled, with pathsin the sense of the trochoidal milling according to the prior art;

FIG. 4 shows the circumferential contact of the milling tool dependenton the milling path radius, as it occurs in the trochoidal millingaccording to the prior art;

FIG. 5 shows a circumferential contact of the milling tool that occursin the trochoidal milling according to the invention; and

FIG. 6 shows paths that occur in the trochoidal milling according to theinvention.

In the following, the present invention will be explained in greaterdetail with reference to the Figures. Before the details of theinventive method will be explained, however, in the following a fewterms will be defined, to which reference will be made later.

The milling machining or processing of the workpiece or the material tobe machined is achieved with the aid of a tool, a so-called miller. Themiller generally has a circular round cross-section with a tool radiusR_(FW).

During the milling, the miller is in engagement with the material. Thecircular arc section of the circular cross-section of the miller, whichis engaged with the material, determines or defines the so-calledcircumferential or wrapping contact of the milling tool.

For the processing or machining of the workpiece, the tool i.e. themiller is moved relative to the workpiece i.e. the material. The motionof the tool i.e. the miller relative to the workpiece is described byso-called tool coordinates, whereby the tool coordinates define theposition of a tool reference point. The motion of the tool referencepoint in the milling machining of the workpiece is designated as thetool path or milling path.

Beginning from a tool tip or peak or from the tool reference point, avector extends along a tool axis or a tool shaft of the tool or miller.This vector along the tool axis beginning from the tool tip or point inthe direction of the tool shaft is referred to as a tool vector.

FIGS. 1 to 4 clarify the relationships in conventional trochoidalmilling, as it is known from the prior art. Thus, FIG. 1 shows a millingtool 10, which penetrates into a workpiece 11 that is to be machined,for the milling machining or processing of the same. The milling tool 10is moved through the workpiece 11 in such a manner that a structuralcomponent with a desired three dimensional free-form surface resultsafter the milling processing or machining.

According to FIG. 1, the milling tool 10 has a circular shapedcross-section with a tool radius R_(FW). In the milling, in order toensure a central rotation of the milling tool 10, the milling tool 10 isrotationally driven about an axis 12 of the milling tool 10. In theconventional trochoidal milling, according to FIG. 1 a reference point13 of the milling tool lying on the axis 12 is moved on a circular path14, whereby this circular path 14 has a radius R_(KB). A translationalfeed advance motion either on a straight or curved feed advance path issuperimposed on these two motions of the milling tool 10. Thesuperposition of these three motions of the milling tool 10 results inthe conventional trochoidal milling according to the prior art, wherebythe milling tool 10 is moved with a radial miller feed or depth of cutA_(E) relative to the workpiece 11.

In the trochoidal milling in the sense of the prior art, thecircumferential contact of the milling tool 10, thus the section of thecircular shaped cross-section of the milling tool that is in engagementwith the workpiece 11 to be milled, is not constant. This can beunderstood especially from FIG. 2, in which the position of the millingtool 10 on the circular path with the radius R_(KB) is entered along theX-axis and the circumferential contact U of the milling tool 10 isentered on the Y-axis. Thus it can be understood from FIG. 2, that thecircumferential contact of the milling tool 10 strongly fluctuatesdepending on the position thereof on the circular path 14.

If the trochoidal milling is used for the production of integral bladedrotors for gas turbines, i.e. of so-called bladed disks (blisks), thusFIG. 3 shows that a flow channel 15 that is to be machined out by meansof the trochoidal milling is bounded by two sidewalls 16, 17 that extendcurved and not parallel relative to one another. From this it followsdirectly that the radius R_(KB) on which the reference point 13 of themilling tool 10 is moved, changes from circular path 14 to circular path14. If, however, the radius R_(KB) of the circular path 14 changes, thisalso has effects or influences on the circumferential contact U of themilling tool as shown by FIG. 4. Thus, once again in FIG. 4, theposition of the milling tool 10 along the circular paths 14 is enteredon the X-axis. The circumferential contact U of the milling tool 10 isagain entered on the Y-axis. FIG. 4 shows the course or progression ofthe circumferential contact of the milling tool dependent on theposition thereof on the circular paths 14 for six different radii. Forradii becoming smaller, the circumferential contact of the milling tool10 changes ever more strongly.

From the above illustrated relationships of the trochoidal milling, asit is known from the prior art, it follows directly, that a maximumpermissible circumferential contact of the milling tool 10, which isgiven or determined in that arising cutting chips need to be surelycarried away, can only be maintained at a certain radius of a path 14and a certain position of the milling tool 10 on this path 14. At allother positions of the milling tool 10 on this path, and at all otherpaths with different radii, in contrast, the circumferential contact ofthe milling tool always lies below the maximum permissible and thusoptimum circumferential contact in the trochoidal milling according tothe prior art.

With the invention a milling method is proposed, in which the trochoidalmilling known from the prior art is optimized in such a manner that anoptimized circumferential contact of the milling tool 10 is ensured,independent of the path on which the milling tool 10 is moved andindependent of the position of the milling tool 10 on the path. Thiswill be explained in greater detail in the following with reference toFIGS. 5 and 6.

It is now in the sense of the present invention, to move the referencepoint of the milling tool no longer on circular paths, but rather moregenerally on curved paths. In that regard, the curvature at each pathpoint of each path is determined in such a manner that an optimizedcircumferential contact of the milling tool is ensured for each pathpoint. For each path point, the circumferential contact of the millingtool is optimized in the direction toward the maximum permissiblecircumferential contact, without exceeding the maximum permissiblecircumferential contact, however.

FIG. 6 shows a flow channel 18 that is to be milled, and that is boundedby two sidewalls 19, 20 that extend curved and not parallel to oneanother. At the beginning or at the start of each path, the milling toolis moved into the material to be milled in such a manner, so that a pathvector of the milling tool, which determines the motion directionthereof, extends in a tangential direction to the sidewall 20 that is tobe nilled-out, and on which the milling process is begun. In thistangential direction, the milling tool is moved into the material solong until the maximum permissible circumferential contact of themilling tool is reached.

After reaching the maximum permissible circumferential contact of themilling tool, the path vector of the milling tool and therewith thecurvature in each path point is adjusted so that preferably in eachsubsequent path point of the path, the maximum permissiblecircumferential contact of the milling tool is ensured or will bemaintained. In that regard, the path vector or the curvature in eachpath point is determined as a function of the tool radius R_(FW) of themilling tool, as a function of the contour of the sidewalls ordepressions that are desired or to be milled, and as a function of theraw part contour or a milling contour of the last completed path. Afterreaching the maximum permissible circumferential contact of the millingtool, this can be maintained for each path point of the path, excludingthe path points that lie at the end of the curved extending paths andalong which the milling tool is moved out of the material to be milledor the workpiece to be machined.

Thus, in a diagram, FIG. 5 shows the circumferential contact that is tobe achieved by means of the inventive method. The position of themilling tool 10 along the path is entered on the X-axis. Thecircumferential contact U of the milling tool 10 is entered on theY-axis. At the beginning of each path, which is illustrated by the point21, the milling tool 10 comes into contact with the workpiece to bemachined, whereby at this point 21 therefore the circumferential contactof the milling tool just still amounts to zero. In this point, themilling tool lies in the tangential direction in contact on the sidewall20 that is to be milled-out. The milling tool is moved into the materialor the workpiece in this tangential direction so long until the maximumpermissible circumferential contact U_(MAX) is reached. This correspondsto the point 22 in FIG. 5. After reaching the maximum permissiblecircumferential contact U_(MAX) in the point 22, the curvature in eachfurther path point is adjusted so that the circumferential contact ofthe milling tool in each further path point corresponds to the maximumpermissible circumferential contact. Only at the end of the curvedextending path, at which the milling tool must be moved out of theworkpiece, and namely in the tangential direction to the other sidewall,the circumferential contact is no longer held to the maximum permissiblevalue thereof, but rather is successively reduced to zero during themoving-out of the milling tool out of the material. This last pathsection, which serves for moving-out the milling tool out of theworkpiece, lies between the points 23 and 24.

FIG. 6 visualizes the curvature progression of several paths 25, whichcan result or arise through the use of the inventive method. Thecurvature progression naturally also depends strongly on the contours ofthe sidewalls that are to be milled-out and therewith on the contour ofthe flow channel that is to be milled-out.

At this point it is again mentioned that naturally also a centralrotation of the milling tool about its tool axis occurs in the inventiveoptimized trochoidal milling during the motion of the tool referencepoint on the curved paths. The motion of the milling tool along thecurved paths 25 and the central rotation thereof are preferably carriedout in opposite rotational directions. This then results in atool-protecting as well as a workpiece-protecting down-cut milling.

Moreover, these two motions are superimposed with a translational feedadvance motion of the tool reference point. As in the conventionaltrochoidal milling according to the prior art, thus also in theoptimized trochoidal milling, three motions are superimposed, namely onthe one hand the central rotation of the milling tool about its axis,the motion of the reference point of the milling tool along the curvedpath, and the feed advance motion of the tool reference point. Incontrast however, in the sense of the invention, the curvature in eachpath point of the paths is optimized such that for each path point anoptimized circumferential contact of the milling tool is ensured.

Necessitated by the fact that thereby the circumferential contact of themilling tool corresponds to the maximum permissible circumferentialcontact in nearly every path point, the maximum possible cutting chipvolume is always or constantly removed and carried away. Thereby, in thesense of the invention, the required milling time can be considerablyreduced by means of the optimized trochoidal milling. Moreover, theoptimized trochoidal milling method has a positive effect on theoperating service life of the milling tool. Namely, the operatingservice life of the milling tool is also determined by the number of thecutting entries or bites of the cutting edge into the material. Sincethe circumferential contact of the milling tool is optimized in thedirection toward the maximum permissible circumferential contact in eachpath point in the inventive milling method, thereby also the number ofthe necessary cutting edge cutting entries or bites into the material isalso reduced. Thereby the operating service life of the milling toolscan also be increased.

The inventive milling method can especially be utilized for theproduction of integral bladed rotors for gas turbines, so-called bladesdisks (blisks) or bladed rings (blinks). It is, however, also suitablefor the milling machining of so-called scallops.

It is further within the sense of the inventive milling method, tosuperimpose a fourth motion component on the above described threemotion components.

Thus, a swinging or pivoting motion of the axis of the milling tool, forproducing a tumbling or wobbling motion with a variable tilt of theaxis, can additionally be superimposed on the motion of the toolreference point along the curved paths, the central rotation of themilling tool about its axis, and the translational feed advance motionof the reference point of the milling tool. This serves for the optimumfitting or close contact of the milling tool to non-vertical sidewalls.For this purpose, the axis of the milling tool can be periodicallypivoted in the sense of a wobbling motion about a defined axis point inthe area of a miller tip or peak of the milling tool, whereby the axistemporarily stands parallel to tangents of the sidewalls that are to bemilled.

1. Milling method for the production of structural components frommaterials that are difficult to machine by chip-cutting, while producingdepressions with at least one sidewall, especially for the production ofintegral bladed rotors for gas turbines, whereby the depressionsespecially form flow channels and the sidewalls especially form bladesurfaces, whereby a milling tool having a tool radius is rotationallydriven about an axis of the milling tool in order to ensure a centralrotation thereof, whereby a reference point of the milling toolpreferably lying on the axis is moved on several curved paths, wherebythe paths preferably comprise different curvatures, and whereby themilling tool is moved with a radial miller feed relative to the materialon the paths, characterized in that the curvature in each path point ofeach path is determined in such a manner that an optimizedcircumferential contact of the milling tool is ensured for each pathpoint.
 2. Method according to claim 1, characterized in that thecurvature in each path point of each path is determined in such a mannerthat for each path point a maximum permissible circumferential contactof the milling tool is not exceeded. 3-10. (canceled)
 11. Methodaccording to claim 1, characterized in that at the beginning or at thestart of each path, the milling tool is moved into the material to bemilled in such a manner, so that a path vector of the milling toolextends in the tangential direction to a sidewall that is to bemilled-out of the structural component that is to be produced, and thatthe milling tool is moved into the material in this direction so longuntil the maximum permissible circumferential contact of the millingtool is reached.
 12. Method according to claim 11, characterized inthat, after reaching the maximum permissible circumferential contact,the path vector of the milling tool and therewith the curvature in eachpath point is adjusted as a function of the tool radius of the millingtool, as a function of the sidewalls or depressions that are to bemilled-out, and as a function of a raw part contour or a milling contourof the last completed path, in such a manner so that approximately ineach subsequent path point of the path the maximum permissiblecircumferential contact of the milling tool is ensured.
 13. Methodaccording to claim 12, characterized in that the maximum permissiblecircumferential contact of the milling tool is ensured in eachsubsequent path point of the path up to and except for an exit region ofthe milling tool out of the material to be milled.
 14. Method accordingto claim 1, characterized in that a translational feed advance motion ofthe reference point of the milling tool is superimposed on the motion ofthe reference point of the milling tool along the optimized curved pathsand the central rotation of the milling tool about its axis.
 15. Methodaccording to claim 14, characterized in that the translational feedadvance motion of the reference point of the milling tool occurs on astraight and/or curved feed advance path.
 16. Method according to claim1, characterized in that the motion of the milling tool along theoptimized curved paths and the central rotation thereof is carried outwith opposite rotation direction.
 17. Method according to claim 14,characterized in that a pivoting motion of the axis of the milling toolfor the production of a wobbling motion with variable tilt of the axisis superimposed on the motion of the reference point of the milling toolalong the optimized curved paths, the central rotation of the millingtool about its axis, and the translational feed advance motion of thereference point of the milling tool.
 18. Method according to claim 17,characterized in that for this purpose, the axis of the milling tool isperiodically pivoted about a point in the area of a miller tip. 19.Milling method for the production of structural components frommaterials that are difficult to machine by chip-cutting, while producingdepressions with at least one sidewall, especially for the production ofintegral bladed rotors for gas turbines, whereby the depressionsespecially form flow channels and the sidewalls especially form bladesurfaces, whereby a milling tool having a tool radius is rotationallydriven about an axis of the milling tool in order to ensure a centralrotation thereof, whereby a reference point of the milling toolpreferably lying on the axis is moved on several curved paths, wherebythe paths preferably comprise different curvatures, and whereby themilling tool is moved with a radial miller feed relative to the materialon the paths, characterized in that the curvature in each path point ofeach path is determined in such a manner so that in each path point thecircumferential contact of the milling tool is optimized to a maximumpermissible circumferential contact.